Chapter 1. Introduction

What is a Telecommuting Module?

A Telecommuting Module is a device which processes traffic under the SIP protocol (see RFC 3261). The Telecommuting Module receives SIP requests, processes them according to the rules you have set up, and forwards them to the receiver.

The Telecommuting Module connects to an existing enterprise firewall through a DMZ port, enabling the transmission of SIP-based communications without affecting firewall security. SIP messages are then routed through the firewall to the private IP addresses of authorized users on the internal network.

The Telecommuting Module can also be used as an extra gateway to the internal network without connecting to the firewall, transmitting only SIP-based communications.

Configuration alternatives

The 3Com VCX IP Telecommuting Module can be connected to your network in three different ways, depending on your needs.

Note that the interface which should receive traffic from the outside must have a public IP address (no NAT), regardless of which Telecommuting Module Type was selected. For a DMZ or DMZ/LAN type, this means that the interface connected to the DMZ of the firewall must have a public IP address.

DMZ Configuration

Using this configuration, the Telecommuting Module is located on the DMZ of your firewall, and connected to it with only one interface. The SIP traffic finds its way to the Telecommuting Module using DNS or by setting the Telecommuting Module as an outbound proxy on the clients.

This is the most secure configuration, since all traffic goes through both your firewall and your Telecommuting Module. It is also the most flexible, since all networks connected to any of your firewall’s interfaces can be SIP-enabled.

The drawback is that the SIP traffic will pass the firewall twice, which can decrease performance.

Fig 1. Telecommuting Module in DMZ configuration.

DMZ/LAN Configuration

Using this configuration, the Telecommuting Module is located on the DMZ of your firewall, and connected to it with one of the interfaces. The other interface is connected to your internal network. The Telecommuting Module can handle several networks on the internal interface even if they are hidden behind routers. No networks on other interfaces on the firewall can be handled.

This configuration is used to enhance the data throughput, since the traffic only needs to pass your firewall once.

This configuration can only support one local network.

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